Just about any chemical poison will kill the lice or mites. It is the dose that you subject the birds to that is critical. Without knowing what shampoo you are planning to use, I can not give you an answer. One important issue is what type of bug do these birds have. It does make a difference in how you treat. Permethrin, carbaryl and DE are all contact killers. that means the bug has to come in contact with a lethal dose of the poison. The trick is to not expose the chicken to a lethal dose too. The Ivomec stuff works through the blood of the chicken and is not effective on all poultry mites/lice.
There are some regions of the country, mostly in the south & south west that have resistant mite populations.
The best advice I can give you to get rid of lice or mites without knowing the type of bug would be to clean out the coop completely. Dispose of the bedding so other birds can't come in contact with it. Get some poultry dust and spread it around in the coop. On and around the roosts. In any cracks and crevices and around the entire perimeter of the coop. Then you need to dust all of your birds. You need to get the dust under the feathers to were the bugs are. I would NOT put any liter in the coop until after the bug problem is solved. You need to dust the birds once a week for three weeks and then check for any bugs. If you still have bugs at that point, you can be certain that you have a resistant strain of bug to the chemical you are using.
What type of spray were you using. Most over the counter sprays are NOT effective killers of parasites. The sprays are generally repellents. They cause the bugs to leave the area for a time and then they return. If you used a bug bomb, those fogger types, you may kill a good number of the bugs, but the majority will not be exposed to a lethal dose and they will escape. Those spray poisons are NOT persistent agents and the bugs will recover and possibly develop a resistance to that poison. Most of these parasites can survive a long time off their host. Some can survive near freezing temperatures for up to a month without a host.
If I knew what type bug you had, I could give you more specific information.
Just so you know I work in the pest control industry. I kill bugs for a living. I would love to be able to help you and your birds. It would be helpful to know what type of coop you have and how big it is. What is in your coop. How many birds do you have. I posted a link earlier in the thread that takes you to a page with pictures of the different types of poultry parasites. If you can determine what type of bug it is, that would help too. Looking at them with a magnifying glass can help. For future reference, you can always collect a sample of the infestation and take it to your county extension office and have them identify it for you.
This is not an easy job, but if you do it right you can get rid of the bugs and with some simple preventive measure you can prevent their return.
Good luck.